Poster Session 213 Structure and Composition of Near-Surface Layers in the Ion-Implanted NiTi Alloy 1 A.D. Pogrebnjak* , **, S.N. Bratushka*, and N. Levintant*** * Sumy Institute for Surface Modification, PO BOX 163, 40030 Sumy, Ukraine, Phone: +380-54-78-39-86, E-mail: apogrebnjak@simp.sumy.ua ** Sumy State University, 2, R-Korsakov str., 40007, Sumy, Ukraine, E-mail: alexp@i.ua *** Institute of Fundamental Technological Research, Warsaw, Poland 1 This work funded by the ISTC Project K-1198. The authors are also thankful to A.P. Kobzev (Joint Institute for Nuclear Physics, Dubna, Moscow Red.) for his help in RBS measurements. Abstract – The surface layer of an equiatomic TiNi alloy, which exhibits the shape memory effect in the martensitic state, is modified with high-dose implantation of 65-keV N + ions (the implantation dose is varied from 10 17 to 10 18 ions/cm 2 ). TiNi samples are implanted by N + , Ni + –N + , and Mo + –W + ions at a dose of 10 l7 –10 18 cm –2 and studied by Rutherford backscattering. scanning electron mi- croscopy, energy dispersive spectroscopy, X-ray diffraction (glancing geometry), and by measuring the nanohardness and the elastic modulus. A Ni + concentration peak is detected between two maxima in the depth profile of the N + ion concen- tration. X-ray diffraction (glancing geometry) of TiNi samples implanted by Ni + and N + ions shows the formation of the TiNi (B 2 ), TiN and Ni 3 N phases. In the initial state, the elastic modulus of the samples is E = 56 GPa at a hardness of H = 2.13 ± 03 GPa (at a depth of 150 nm). After double implantation by Ni + –N + and Mo + –W + ions, the hardness of the TiNi samples is 2.78 ± 0.95 GPa at a depth of 150 nm and 495 ± 2.25 GPa at a depth of 50 nm; the elastic modulus is 59 GPa. Annealing of the samples at 550 °C leads to an increase in the hardness to 4.44 ± 1.45 GPa and a sharp increase in the elastic modulus to 236 ± 39 GPa. A correla- tion between the elemental composition, micro- structure, shape memory effect, and mechanical properties of the near-surface layer in TiNi is found. 1. Introduction The passage of medium-energy ions through solids is known to be accompanied by their scattering by host atoms and electrons [1, 2], which results in the retar- dation of ions, a change in the ion motion direction, the displacement of host atoms from lattice sites, the accumulation of impurities in the target, sputtering of the material surface, atomic mixing, the formation of a concentration profile of implanted ions, and the for- mation of new phases. These factors substantially af- fect the physicomechanical and chemical properties of implanted materials [1–4]. High-dose intense implan- tation leads to a shift in the maximum in the concen- tration profile of implanted ions to the surface because of intensified scattering processes [3, 4]. High-dose intense implantation is considered to be ion implanta- tion such that the dose accumulation rate is about 10l6 cm –2 /min and the concentration of implanted ions is several tens (up to 100) of atomic percent [5–7]. The application of high-dose intense implantation leads to an increase in the ion (mainly N + ion) penetra- tion depth; intensified scattering of the surface layer; a shift in the maximum, concentration, and shape of the concentration profile; and many other processes that are weakly pronounced during low-intensity ion im- plantation at low doses (several units of atomic proc- esses) of implanted ions [1, 2, 5]. On the other hand, TiNi-based alloys belong to the group of materials in which a high-temperature phase with a B 2 structure undergoes a shear or martensitic phase transformation as the temperature changes or a stress is applied. The atomic restructuring in TiNi-based alloys is accompa- nied by both martensitic anelasticity effects and a change in their surface state, which is caused by the complex structure of the martensite phase in them [8- 11]. As a result, a developed martensitic relief with a large number of various interfaces appears, which should affect both the electrochemical and corrosion properties and the plasticity and strength properties of these materials. As a method of surface alloying, ion implantation of a surface can strongly affect the struc- tural parameters and stability of the B 2 phase in the near-surface layers and, hence, the following set of its properties: the martensite transformation temperature, the martensite anelasticity parameters, the shape memory effect (SME), and superplaslicity. As a result, it can change the deformation relief, the cracking con- ditions, and the electrochemical and corrosion proper- ties [12–18]. Therefore, double implantation of N + and Ni + ions into TiNi is of particular interest, since the implantation of Ni + ions changes the equiatomic com- position of the alloy and. in combination with N + ions, hardens the surface layer and. correspondingly, modi- fies the physicomechanical and chemical properties [18–20]. The effect of N + ions on the mechanical properties of steels and alloys is well known. The alloying of steels and alloys with elements such as W and Mo is widely used to improve their mechanical